Han Yu, Wang Xiaodong, Wang Wei, Lee Yuan Xien, Li Ao
School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110819, China.
School of Mechanical and Electrical Engineering, Chuzhou University, Chuzhou 239004, China.
Micromachines (Basel). 2023 Jun 16;14(6):1260. doi: 10.3390/mi14061260.
Micro-cooling systems are compact refrigeration systems widely applicable in microchemical analysis, biomedicine, and microelectromechanical systems (MEMS). These systems rely on the use of micro-ejectors to achieve precise, fast, and reliable flow and temperature control. However, the efficiency of micro-cooling systems is hindered by spontaneous condensation occurring downstream of the nozzle throat and within the nozzle itself, impacting the performance of the micro-ejector. A micro-scale ejector mathematical model describing wet steam flow was simulated to investigate the steam condensation phenomenon and its influence on flow, incorporating equations for liquid phase mass fraction and droplet number density transfer. The simulation results of wet vapor flow and ideal gas flow were compared and analyzed. The findings revealed that the pressure at the micro-nozzle outlet exceeded predictions based on the ideal gas assumption, while the velocity fell below it. These discrepancies indicated that condensation of the working fluid reduces the pumping capacity and the efficiency of the micro-cooling system. Furthermore, simulations explored the impact of inlet pressure and temperature conditions on spontaneous condensation within the nozzle. The results demonstrated that the properties of the working fluid directly influence transonic flow condensation, underscoring the importance of selecting appropriate working fluid parameters for nozzle design to ensure nozzle stability and optimal micro-ejector operation.
微冷却系统是紧凑的制冷系统，广泛应用于微化学分析、生物医学和微机电系统（MEMS）。这些系统依靠微喷射器来实现精确、快速和可靠的流量及温度控制。然而，微冷却系统的效率受到喷嘴喉部下游及喷嘴内部自发冷凝现象的阻碍，影响了微喷射器的性能。为了研究蒸汽冷凝现象及其对流动的影响，模拟了一个描述湿蒸汽流动的微尺度喷射器数学模型，该模型纳入了液相质量分数和液滴数密度传递方程。对湿蒸汽流动和理想气体流动的模拟结果进行了比较和分析。研究结果表明，微喷嘴出口处的压力超过了基于理想气体假设的预测值，而速度则低于预测值。这些差异表明，工作流体的冷凝降低了微冷却系统的泵送能力和效率。此外，模拟还探讨了入口压力和温度条件对喷嘴内自发冷凝的影响。结果表明，工作流体的特性直接影响跨音速流动冷凝，这突出了为喷嘴设计选择合适的工作流体参数以确保喷嘴稳定性和微喷射器最佳运行的重要性。
